Methods, apparatus, and systems for occluding a tissue opening are provided. One embodiment includes a catheter having an elongate body and a first lumen to direct hypertonic saline through an opening in the lumen to tissue of a fossa ovalis. The embodiment includes a radiofrequency (RF) electrode coupled to the elongate body proximal a distal end of the elongate body. The RF electrode can emit RF energy to the tissues of the passage and the hypertonic saline can facilitate a distribution of the RF energy along the tissue to fuse the tissue of the passage.